Kenwood NX-800 Service Manual page 30

NX-800
LPF (IC702) works as smoothing fi lter. The DAC (IC712)
assigns the base band signal to the VCO and VCTCXO (X1).
At this time, the level output according to the transmit car-
rier is fi ne-adjusted according to each modulation method.
4-3. Drive and Final amplifi er
The transmit signal obtained from the TX VCO buffer
amplifi er Q9, is amplifi ed to approximately +17dBm by the
driver amplifi ers Q10, Q101 and Q102.
This amplified signal is passed to the power amplifier
module (power module) IC102, which consists of a MOS-
FET amplifi er and capable of transmission output power.
4-4. APC circuit
The Automatic transmission power control (APC) circuit
stabilizers the transmitter output power at a predetermined
level by detecting the power module output with a diodes
D108, D109 and D111. Diodes D108, D109 and D111 apply
a voltage to DC amplifi er IC103 (1/2).
IC103 (2/2) compares the APC control voltage (PC) gen-
erated by MCU IC510 and DC amplifier IC101 (1/2, 2/2)
with the detection output voltage from IC103 (1/2) to control
the Vgg Pin of IC102, and stabilizes transmission output.
The APC circuit is confi gured to protect over-current of
the power module due to fluctuations of the load at the
antenna end and to stabilize transmission output at voltage
and temperature variations.
TX VCO
MOD
VCTCXO
MB
19.2MHz
30
CIRCUIT DESCRIPTION /
Optional Scrambler Board
D703,D704
Q705,Q706
INT. MIC Q707
SW AGC
MM
LPF LPF AMP
IC702 IC702 IC709
(2/2) (1/2) (1/2)
0dBm
Buff AMP Drive AMP Drive AMP
Q9 Q10 Q101
电路说明
LPF(IC702) 用作平滑滤波器。DAC(IC712) 将基带信号分配
到 VCO 和 VCTCXO(X1)。此时，将按照各自的调制方式对按照
发射载波输出的电平进行微调。
IC706 IC706
(1/2) (1/2)
IC708
SW AMP LPF
SCSW
IC1
IC712 AMP
AMP
IC5 (2/2)
Fig. 5 / 图 5
4-3. 驱动及末级功率放大器电路
驱动放大器 Q10、Q101 和 Q102 将从 TX VCO 缓冲放大器 Q9
获得的发射信号放大 +17dBm 左右。
放大后的信号转到功率放大器模块 ( 功率模块 ) I C102( 由
单个 MOS-FET 放大器组成并能发射输出功率 )。
4-4. APC 电路
通过使用二极管 D108、D109 和 D111 检测功率模块输出，
自动发射功率控制 ( A P C ) 电路将发射器输出功率稳定在预定
电平。二极管 D108、D109 和 D111 对直流放大器 I C103(1/2)
施加电压。
IC103(2/2) 将 MCU IC510 和直流放大器 IC101(1/2，2/2)
生成的 A P C 控制电压 ( P C ) 与 I C103(1/2) 的检测输出电压进
行比较， 从而达到控制 IC102 Vgg 针脚并稳定发射输出的目的。
配置 A P C 电路是为了保护因天线端负载波动而引起的功率
模块过流，以及在电压和温度变化时稳定发射输出。
+17dBm
Drive AMP Final AMP
Q102 IC102
Gate
bias
PC
DC DC
AMP AMP
MP
IC101 IC103
Fig. 6 / 图 6
IC502
DSP
IC510
X1
VCTCXO
VCO
D103,D104,
D106,D216
SW ANT Filter
D108 D109 D110
DET DET DET
ANT